COMPOSITE FIBERS OF ALKALI METAL HEXATITANATE AND RUTILE TiO{11

ABSTRACT

A fibrous material is provided which is composed of composite fibers having a number average diameter of up to about 10 microns and an average length/diameter ratio of at least about 5/1. The fibers have a core of alkali metal hexatitanate encapsulated by a shell of rutile TiO2 and are essentially inert to aqueous 5% by weight HF solution. The fibrous material is particularly useful in the reinforcing of plastics.

United States Patent [191 Emslie, deceased COMPOSITE FIBERS OF ALKALIMETAL HEXATITANATE AND RUTILE TH);

[75] Inventor: Robert Steele Emslle. deceased, late of Chadds Ford, Pa.by Jean McPhaul Emslie, administratrix [73] Assignee: E. l. DuPont deNemours and Company, Wilmington. Del.

[22] Filed: Apr. 6, 1972 [2i] Appl. No.: 241,681

[52] US. Cl. 106/300, l06/308 B [5] Int. Cl. C091: 1/36 [58] Field ofSearch 106/300. 308 B [56] References Cited UNITED STATES PATENTS3338.677 8/l967 Berry 106/300 l Dec. 18, 1973 3,703.357 ll/l972 Surls etal. l06/300 Primary Examiner-Curtis R. Davis Al!orneyDonald A. Hoes [S7] ABSTRACT A fibrous material is provided which is composed ofcomposite fibers having a number average diameter of up to about 10microns and an average length/diameter ratio of at least about 5/1. Thefibers have a core of alkali metal hexatitanate encapsulated by a shellof rutile TiO, and are essentially inert to aqueous 5% by weight HFsolution. The fibrous material is particularly useful in the reinforcingof plastics.

1 Claim, 1 Drawing Figure l5 MICRONS COMPOSITE FIBERS OF ALKALI METALHEXATTTANATE AND RUTILE T102 BACKGROUND OF THE INVENTIONWater-insoluble, fibrous alkali metal titanates having the formula MO(TiO where M is an alkali metal of atomic number of at least I l, and nis a number of from 4 to 8 and their preparations are disclosed in U.S.Pat. Nos. 2,833,620, Gier et al.; 2,841,470, Berry; 3,328,117, Emslie etal.; and 3,33l,658, Lewis et al.

The preparation of fibrous titanium dioxide is described in U.S. Pat.Nos. 3,0l2,857, Pease; 3,065,091, Russell; 3,24l,928, Pease; and3,244,481, Berry.

Also mixtures of pigmentary titanium dioxide and fibrous alkali metaltitanates are disclosed in U.S. Pat No. 3,484,260, Emslie et al.

These fibrous materials are useful as reinforcing components forplastics, ceramics and cermets. Other uses include insulation materialsand additives during paper manufacture.

It is known that fibrous titanates will tend to deteriorate in certainacid atmospheres and that improvements in this and other propertieswould be desirable.

SUMMARY OF THE INVENTION In accordance with the invention there isprovided a fibrous material composed of composite fibers having a numberaverage diameter of up to about 10 microns and an averagelength/diameter ratio of at least about 5/1, said fibers having a corecomposition corresponding to the formula wherein M is an alkali metal ofatomic number of at ieast 1 1, said core being encapsulated by a shellof rutile TiO thereby rendering the fibers essentially inert to aqueousby weight HF solution.

The individual composite fibers possess the combined strength of thealkali metal hexatitanate and rutile components. In addition they tendto be less expensive to prepare, more dense, and more stable to acid andelevated temperatures than are the alkali metal titanates. It is known,for example, that when ordinary potassium titanate fibers are heated toa temperature over 900 C., they start to lose potassium oxide and somestrength. The rutile titanium dioxide shell of the composite fibers ofthe present invention minimizes the loss of alkali at high temperatures.Since the outer shell of these composite fibers is rutile titaniumdioxide, the fibers are characterized by the higher refractive index oftitanium dioxide, i.e. the refractive index of rutile TiO is about 2.7]compared to the refractive index of potassium titanate which is about2.35. This higher refractive index of the composite fibers is importantwhen the fibers are to be used in a system where high opacity is adesired characteristic.

The presence of the alkali metal hexatitanate and rutile TiO componentsin the composite fibers can be readily confirmed by X-ray analysistechniques as both components are characterized by distinct X-raydiffraction patterns. The existence of the core/shell compositestructure is readily confirmed by treating the fibers with a 5% byweight HF solution. A true composite is virtually unaffected by thetreatment since rutile TiO is essentially inert to the action of 5% oreven HF solution. If the fibers were a homogeneous mixture of alkalimetal hexatitanate and rutile TiO or if the alkali metal hexatitanatewas otherwise in the shell portion, considerable dissolution and weightloss would occur.

The actual percentage of rutile TiO as a shell about the core of alkalimetal hexatitanate is not critical pro vided that the amount be such asto ensure inertness to the action of 5% by weight HF solution. Normallythe alkali metal titanate should constitute at least l0% and, preferablyat least 50%, by weight of the composite fibers.

The fact that the TiO shell about the alkali metal hexatitanate core isin the rutile crystalline phase serves to distinguish the products ofthe invention from prior art products in which alkali metal titanatefibers may have been leached with acid to remove a portion of the alkalimetal oxide from the surface; i.e. such leaching would not result in adistinct TiO shell of the rutile crystalline phase.

Various processes can be used for preparing the composite fibers. Onetechnique, to be described in Example l hereinafter, involves thepreparation of alkali metal titanate fibers in the usual way. This maybe accomplished, for example, by calcining a dry blended mixture ofanatase TiO alkali metal carbonate and alkali metal halide followed byleaching of the calcined product to remove soluble salts. The resultantalkali metal titanate fibers can then be converted to composite fibersby calcining, for example, at 1,000 C., in the presence of a boronorsilicon-containing compound such as Na, 8 0 K B 0 B 0 Na SiO muscovitemica, or feldspar. The composite fibers form directly, apparently as aresult of the reaction of the boronor silicon-containing compound withthe alkali metal oxide in the surface portion of the alkali metaltitanate fibers.

Alternatively, alkali metal titanate fibers may be initially formed bythe procedure described above but with the inclusion of one of theaforementioned boronor silicon-containing compounds in the dry blendedmix before calcining. This method is illustrated in Example llhereinafter.

Still a third method, and one which wqll be illustrated in Examples lllthrough V hereinafter, involves direct formation of the composite fibersfrom a mixture of an alkali metal hydroxide, titanium oxychloride, andone of the silicaor boron-containing compounds described above. In thiscase, a salt-gel is formed of the various components, which is calcinedat a temperature of 850 C. to 1,050" C. More particularly, the salt-gelis prepared by admixing concentrated aqueous alkali metal hydroxidesolution, e.g. KOH or NaOH, and aqueous titanium oxychloride solution(e.g. as prepared from the reaction of TiCl, and ice), the mixingpreferably being carried out by means of a high speed, high shear mixer.In the process, one solution is conveniently added to the other inrelative amounts such that a pH of at least 9, preferably of l0-l 0.5,is reached, at which point a thick salt-gel is formed. The salt'gel isthen cast in a suitable container and, preferably, dried. The resultantporous brick is subsequently calcined at a temperature in the range from850 C. to L050 C. and then leached, e.g. with water or aqueous liquids,to produce the composite fibers.

Regardless of the method employed, simple leaching of the resultantfibers appears to remove essentially all residual compounds containingboron or silicon. Thus, borates tend to be converted to higher boratesin the process and these are generally soluble in the water used as aleaching agent. Where a silicon-containing compound has been employed,the use of an aqueous HP leaching solution may be necessary to removeun' desired silicate byproducts.

The amount of boron or silicon-containing compound that need be soemployed will vary depending upon which particular process is selected.Moreover, the amount will affect, at least to some extent, the thicknessof the TiO shell which is formed. Too little may result in an undulythin TiO shell, which in turn may fail to give the requisite inertnessto a HF solu' tion. Large quantities of the boronor silicon containingcompound will, conversely, tend to produce a relatively thick shell ofTiO This is not particularly detrimental, however, except from thestandpoint that the economics may be less favorable. In general, it issatisfactory to employ some 5 to 50% by weight of the boronorsilicon-containing compound based on the weight of the composite fiberwhich is formed.

Each of the processes results in a composite fiber in which the titanateis essentially in the hexa-crystalline form. apparently because thatspecies is the most thermally stable species.

The utility of the composite fibers will depend, at least in part, upontheir particle size. Smaller size particles, say of 0.1 to 0.6 micron indiameter, are useful for the pigmentation of paper, plastics, fibers andthe like. Larger size particles, most commonly of 0.6 to 3 microns indiameter, but occasionally up to microns in diameter, are useful in thereinforcement of plastics or as insulation materials. In general thecomposite fibers should have aspect ratios, i.e. L/D ratios of at least5 to l but more preferably to l. Aspect ratios of l00-l,000 to l are notuncommon.

DESCRIPTION OF THE DRAWING FIG. 1 is a photomicrograph at 4,200X ofcomposite t\ Ti,,() rutile fibers prepared by the salt-gel method ofExample IV with the incorporation of both gotassium borate and paperpulp in the reaction mixture.

EXAMPLES To illustrate the invention more completely, the followingexamples are given. These are for purposes of illustration only and arenot to be construed as limitalion of the invention.

EXAMPLE I Pigmentary size fibers of potassium titanate are produced bythe general procedure described in Emslie et =1l. US. Pat. No. 3,328,ll7 involving the calcination of potassium carbonate, anatase TiO andKCl.

A 04 gr. portion of the potassium titanate fibers are wet mixed with 0.6gr. of wet ground plate glass (silicate glass). The mixture is thendried and placed in a furnace. The temperature is raised to 900 C. overa period of about 2 hours and kept at that temperature for hour. Theproduct is removed from the furnace, and eached in 5% by weight HF withagitation for 3 days. After settling, decanting the clear liquor,filtering, washing with water and drying, the product is subjected toanalysis.

Xray analysis demonstrates that the product is composed of K 'li o andrutile TiO, in a ratio estimated 0 be about if]. Microscopically thefibers are found to have an L/D ratio of about l00:l. They are in thepig mentary range, i.e. with a fiber diameter of about (H to 0.6microns. The core/shell structure is confirmed by the inertness to 5% byweight HF solution in water.

EXAMPLE II A blend is prepared by micronizing together the followingcomponents:

300 grams anatasc TiO, I00 grams K,CCi

200 grams KCl The mixed powder is then added to wet paper pulp I00 gramstotal weight 20% paper pulp fibers) and rolled in a four liter vesselfor l hour. Balls form that are about l2 cm. in diameter and are made upof the paper pulpingredient mixture. These balls are calcined for 2hours at ],000 C. The composite fibers are then recovered by leachingaway the soluble salts with dilute sulfuric acid.

Microscopically the product is found to have an average length of about10 microns, an average diameter of about 0.1 to 0.2 micron and a surfacearea of 7.3 M lg. The fibers are found to be composed of a predominatelypotassium hexatitanate core and an outer rutile TiO shell.

EXAMPLE III Fifty grams of KOH is added to 50 cc. distilled water toprepare a concentrated KOH solution which is then placed in a WaringBlendor along with 15 grams K B O While agitation is maintained, atitanium oxychloride solution (considered to be represented by theformula TiOCI- 'ZHCI) is added until a pH of 10 is reached. The titaniumoxychloride solution is prepared by mixing TiCl and ice in a 31'] weightratio. The amount of titanium oxychloride solution so required is 150grams.

The salt-gel thus prepared is cast into a glass vessel lined withpolytetrafluoroethylene and dried for 4 hours at 200 C. A porous brickis formed which is then calcined for minutes at 900 C.

The calcined brick is leached free of soluble salts by washing with hotdistilled water. Fourteen grams of a fibrous product are therebyobtained. X-rays reveal that the product, which has a surface area of9.5 Mlgn, contains both rutile and potassium hexatitanate. Examinedmicroscopically, the composite fibers are found to have an averagediameter of about 0.1 micron and an L/D ratio of about 200.

Five grams of the product is placed in 10% aqueous hydrogen fluoridesolution in a polyethylene beaker. After 2 hours of stirring, thefibrous product is recovered, washed with distilled water, and dried. Itis found to be essentially unchanged. This demonstrates that the rutileeffectively encapsulates a potassium hexatitanate core since it is knownthat potassium titanate alone would be completely soluble in 10%hydrogen fluoride solution.

EXAMPLE IV The procedure is the same as that of Example III except that10 grams of wet paper pulp (20% solids) is added to the KOH solutionalong with the 15 grams of K B O In this case the potassiumhexatitanatel'l'iO composite fibers have a surface area of 17 M /gr. andlength and diameter dimensions similar to the fibers of Example [11.FIG. 1 is a photomicrograph of the fibers at 4,200x.

EXAMPLE V Fifty grams of KOH is added to 50 cc. distilled water toprepare a concentrated KOH solution. The concentrated KOH solution isplaced in a Waring Blendor along with grams of wet paper pulp (20%solids) and 10 grams of a titanium oxychloride solution prepared as inExample Ill. While agitation is maintained, more of the titaniumoxychloride solution is added until a pH of 10 is reached, thisrequiring grams of the solution.

The salt-gel thus prepared is cast and dried as in Example lll. Theporous brick thus formed is subsequently calcined for 1 hour at 950 C.

The calcined brick is leached free of soluble salts by washing with hotdistilled water. A 10% hydrogen fluoride solution is then used over aperiod of 2 hours to dissolve away the silicates generated in thecalcination step. The treatment otherwise leaves the fibers essentiallyunchanged.

The recovered composite fibers have a surface area of l5 Mlgr. andX-rays reveal the presence of both rutile and potassium hexatitanatecomponents. The fibers have length and diameter dimensions similar tothose of Example Ill.

EXAMPLE VI Composite fibers prepared by the methods described inExamples II and III are tested for their reinforcing strength in acommercial, high density, linear polyeth- FLEX TEST RESULTS Sample FlexStrength-psi Flex Moduluspsi Control No fiber reinforcement 4.500150,000 Example ll fibers 7,320 1 290 594,000 1* 40,000 Example IIIfibers 6,450 :2 230 427,000 1 17,000

What is claimed is:

l. A fibrous material composed of composite fibers having a numberaverage diameter of up to about l0 microns and an averagelength/diameter ratio of at least about Sll, said fibers having a corecomposition corresponding to the formula wherein M is an alkali metal ofatomic number of at least 1 1, said core being encapsulated by a shellof rutile TiO, thereby rendering the fibers essentially inert to aqueous5% by weight HF solution.

I I I I.

